The present invention relates to a select shock attenuating method and system for an automatic transmission. The term "select shock" is used hereinafter to mean shock occurring in an automatic transmission during transition from neutral to any one of torque transmitting drive states.
U.S. Pat. No. 4,730,521 issued to Hayasaki et al. on Mar. 15, 1989 discloses an automatic transmission comprising a plurality of hydraulically actuable and frictionally engageable couplings, a hydraulic control system including a pressure regulator valve and a manual valve, and a control unit. A pressure regulator valve effects pressure regulation by generating line pressure under the control of an actuator in the form of a solenoid actuable actuator, also referred to as a line pressure solenoid. The manner of controlling the magnitude of the line pressure is well understood from claims 1 to 7 of U.S. Pat. No. 4,807,496 issued to Hayasaki et al. on Feb. 28, 1989. The control unit is programmed to condition the hydraulic control system in one state wherein hydraulic fluid under the line pressure is supplied to one of the plurality of hydraulically actuable and frictionally engageable couplings to establish one gear ratio after a manual selector valve has been placed to a forward drive range position from a neutral range position. After placing the manual selector valve to a reverse drive range position from the neutral range position, the control unit conditions the hydraulic control system in another state wherein hydraulic fluid under the line pressure is supplied to two of the plurality of hydraulically actuable and frictionally engageable couplings to establish another gear ratio.
Japanese Patent Application First (unexamined) Publication No. 3-28571 proposes a system for attenuating select shock which occurs during a transition after a manual selector valve has been placed to a forward drive range position from a neutral range position. According to this known system, the line pressure is momentarily increased toward a precharge level and then subject to an increase at a gradual rate. The precharge level and the rate of increase are determined after considering a stroke volume of a servo piston and torque bearing capacity of a hydraulically actuable and frictionally engageable coupling to be actuated.
An object of the present invention is to provide an improved control method and system which reduces the generation of shock tending to occur during a transition to any of available drive states from a neutral state in an automatic transmission.